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luaescapinglua-patterns

What is the proper Lua pattern for quoted text?

I've been playing with this for an hour or tow and have found myself at a road block with the Lua pattern matching utilities. I am attempting to match all quoted text in a string and replace it if needed.

The pattern I have come up with so far is: (\?[\"\'])(.-)%1

This works in some cases but, not all cases:

Working: "This \"is a\" string of \"text to\" test with"

Not Working: "T\\\"his \"is\' a\" string\" of\' text\" to \"test\" wit\\\"h"

In the not working example I would like it to match to (I made a function that gets the matches I desire, I'm just looking for a pattern to use with gsub and curious if a lua pattern can do this):

 string
 a" string" of
is' a" string" of' text
test
his "is' a" string" of' text" to "test" wit

I'm going to continue to use my function instead for the time being, but am curious if there is a pattern I could/should be using and i'm just missing something with patterns.

(a few edits b/c I forgot about stackoverflows formating) (another edit to make a non-html example since it was leading to assumptions that I was attempting to parse html)

Solution

  • Trying to match escaped, quoted text using regular expressions is like trying to remove the daisies (and only the daises) from a field using a lawnmower.

    I made a function that gets the matches I desire

    This is the correct move.

    I'm curious if a lua pattern can do this

    From a practical point of view, even if a pattern can do this, you don't want to. From a theoretical point of view, you are trying to find a double quote that is preceded by an even number of backslashes. This is definitely a regular language, and the regular expression you want would be something like the following (Lua quoting conventions)

    [[[^\](\\)*"(.-[^\](\\)*)"]]

    And the quoted string would be result #2. But Lua patterns are not full regular expressions; in particular, you cannot put a * after a parenthesized pattern. So my guess is that this problem cannot be solved using Lua patterns, but since Lua patterns are not a standard thing in automata theory, I'm not aware of any body of proof technique that you could use to prove it.